Low voltage under water wiring

[bernardgreen]

SWA under the road which was always (by intent) carrying mains voltage, would we?

Those cables are shown on utility company maps and even then any one digging in the highway will be careful about the possibility of errors / omissions in the maps.

Unless the private (DIY ) power cable installed though the culvert is added to the drainage maps anyone working on the culvert will not be aware of the cable.

Would this situation not trip the consumer unit?

It would be very unlikely to trip any thing ( RCD or MCD ) in the the consumer unit due to the isolation provided by the power supply unit.

 

[keenamateur123]

Would I be overall safer using a kit like Philips hue and using their pre-made cabling and transformer?

It runs 24v and 70w?

https://www.philips-hue.com/en-gb/p/hue-white-and-colour-ambiance-lily-outdoor-spot-light/1741830P7

Would this be overall safer? I could put some plastic conduit to run the wire through at the top of the culvert? The culvert is 2 feet in diameter and the water flowing through it is usually about 3 inches deep so I'm not worried about obstruction due to the cable.

Given that we maintain the culvert, the inflow and outflow at both sides etc I'd imagine quite low risk from a person going in? I'd also be planning to have the entire set up on a timer that would only come on at night, minimising the risk of anyone being in the water for any reason?

 

[ebee]

On an open cut / in water/ on a bad day then a 24v tingle and a 12v tingle or a six volt tingle might have a bit more tingle in some ways. of course if you half the voltage you double the current for a given load but a source with a xxx amps/milliamps can draw up to and over its stated rating anyway. LEDs can be made in a way that uses a constant current source (limit) so that might actually help or not.

I am not saying don`t do it, even with mains voltages, I`m just suggesting covering all angles you might not have allowed for.

 

[keenamateur123]

On an open cut / in water/ on a bad day then a 24v tingle and a 12v tingle or a six volt tingle might have a bit more tingle in some ways. of course if you half the voltage you double the current for a given load but a source with a xxx amps/milliamps can draw up to and over its stated rating anyway. LEDs can be made in a way that uses a constant current source (limit) so that might actually help or not.

I am not saying don`t do it, even with mains voltages, I`m just suggesting covering all angles you might not have allowed for.

Oh I'm very grateful for all the advice, I'm just trying to put something together that minimises all of these possible problems. Please don't take anything I've said as any sort of criticism or ingratitude.

I was thinking of using the Philips out instead with conduit rather than making something myself purely to try and minimise risk. I thought with the power supply being limited to 100w @24v and coming as a complete kit from a reputable company it might mitigate some of the risk from the electrics?

Rather hoping someone can give me a 'just do it this way' type answer as I'm getting a bit stuck!

I wouldn't be comfortable with mains voltage personally in this situation, hence why trying to use low voltage equipment

 

[JohnW2]

.... I could put some plastic conduit to run the wire through at the top of the culvert? The culvert is 2 feet in diameter ....

Given that some people here seem concerned about workers (presumably dwarf ones ) not being aware of the presence of the cable (which ought not to be a hazard for them anyway), it might perhaps be better to not use conduit, so that it could be clearly seen that thee cable was a cable?

I have to say that, other than for possible legal/bureaucratic issues (about which I know little/nothing), it seems to me that this who exercise is being seriously "over-thought"

Kind Regards, John

 

[Harry Bloomfield]

I certainly coult use 12v instead, although the kits I had looked at had been 24v. Is there a clear advantage of 12v?

The lower the voltage, the more the voltage drop becomes a thing to be considered.

 

[JohnW2]

The lower the voltage, the more the voltage drop becomes a thing to be considered.

Indeed, and it's a 'double whammy'. ... for a load of a given power, lower voltage means higher current and hence a higher (absolute) voltage drop, but that 'higher VD' becomes even more relevant (i.e as a percentage of the supply voltage) because the supply voltage is lower.

Kind Regards, John

 

[securespark]

Increase the c.s.a.?

 

[SUNRAY]

...

I have to say that, other than for possible legal/bureaucratic issues (about which I know little/nothing), it seems to me that this who exercise is being seriously "over-thought"

Kind Regards, John

In some ways yes, however it's good to see the question being raised before the event.

Aquatic accessories have for decades been 24V SELV (safe extra low voltage and basically the methods Bernard describes) and classed as livestock friendly.
For what it's worth I knew of a pond that had 2 pumps on the same 24Vac supply for years, except the owner didn't know there was a second pump until they cleaned the overgrown end of the pond and caught the cable with a rake or something similar. the second pump was totally rusted up solid and full of water, the cable joint was a bit of choc block wrapped with plastic tape and totally not waterproof. There were lots of fish, frogs and other livestock which didn't appear to be stressed and bred copiously every year to the point they sold some on a regular basis and let local children tape tadpoles, also a Heron was a regular visitor for lunch.
Our electric shock points raised have been related to the possibility of the SELV being raised to mains potential under fault conditions. One way round that may be to use PELV (Prodected ELV) where the ELV circuit is earthed, however that could theoretically introduce other issues.



Ebee raises a point about current increasing with lower voltage and greater voltage drop. In my garden I have 12vac lighting bollards which started as a mixture of 8W and 21W fittings totalling 120W and the furthest point from the transformer being ~30m, the difference in brightness and colour was quite apparent using the original 1.15mm² supplied despite being less than a volt different. Basically I upgraded everything to at least 2.5mm² and the longer parts to 6mm² and 10mm² (Offcuts of tri-rated single I had to hand mostly).

Depending on the length of your armoured cable (yes I would suggest it's what you use) I'd advise to go bigger. We can do the voltage drop calculations if required.

EDIT: the previous 3 messages weren't there when I started this reply.

 

[mattylad]

What is the diameter of this pipe?
Is it big enough to crawl through? (and thus allow you to fasten it to the top section all the way along).
Can you put it in another pipe that is then fed through without blocking the pipe?

 

[SUNRAY]

What is the diameter of this pipe?
Is it big enough to crawl through? (and thus allow you to fasten it to the top section all the way along).
Can you put it in another pipe that is then fed through without blocking the pipe?

... The culvert is 2 feet in diameter and the water flowing through it is usually about 3 inches deep so I'm not worried about obstruction due to the cable.

...

 

[mattylad]

I missed that, so in that case someone can crawl through and attach one of those ribbed pipes to the top so that a cable can be pulled through it and the ends filled with wire wool & foam to stop critter entry?

 

[JohnW2]

In some ways yes, however it's good to see the question being raised before the event.

Aquatic accessories have for decades been 24V SELV (safe extra low voltage ....

"Separated extra-low voltage" ('separated' from earth), actually, as opposed to PELV ('Protective extra-low voltage'), which is not separated from earth.

Kind Regards, John

 

[SUNRAY]

"Separated extra-low voltage" ('separated' from earth), actually, as opposed to PELV ('Protective extra-low voltage'), which is not separated from earth.

Kind Regards, John

Oh my goodness what a silly mistake, but I plead insanity on the grounds a bloke I worked with a lot always called it 'safe'.
When talking with customers it very likely made more sense too.

 

[ebee]

I think that some years ago it was called Safety instead of Separated